Method of oxidizing tin and treatment

ABSTRACT

A method of plating metallic articles with tin in which the tin, after plating, is treated to render it readily oxidizable. The method also includes the step of oxidizing the tin so treated and, if desired, of removing some of the oxidation to produce an effect of highlights and relatively darker portions, sometimes called &#39;&#39;&#39;&#39;antiquing&#39;&#39;&#39;&#39;.

nited States Patent [191 Schubert Oct. 23, 1973 METHOD OF OXIDIZING TIN AND TREATMENT [75] Inventor: Walter A. Schubert, Elgin, Ill.

[73] Assignee: Elgin Metal Casket Company, Elgin,

lll.

[22] Filed: Oct. 27, 1971 [21] Appl. No.: 193,150

Related US. Application Data [63] Continuation-in-part of Ser. No. 812,341, April 1,

1969, abandoned.

[52] US. Cl. 148/6.14, 204/36 [51] Int. Cl C23c 1/04, C23b 3/06 [58] Field of Search l48/6.l4, 6.24, 20.6;

[56] References Cited UNITED STATES PATENTS 3,577,282 5/l97l Schubert 148/624 Pearson et al. l48/6.l4 R X Glock 204/36 X Primary Examiner-Alfred L. Leavitt Assistant Examiner-M. G. Wityshyn Attorney-Howard T. Markey et al.

57 1 AliSTRACT 5 Claims, No Drawings METHOD OF OXIDIZING TIN AND TREATMENT This is a continuation-in-part of my co-pending appli-' cation Ser. No. 812,341, filed Apr. 1, 1969, now abandoned.

BACKGROUND OF THE INVENTION In the past, it has been common to plate metal hardware articles such as handles, knobs and levers with silver, which is a metal readily oxidizable. The silver plated parts, when oxidized, have in frequent usage been further treated by polishing, or buffing or by abrasion generally to remove some of the oxidized silver plate and thereby to produce a desired effect in which light and dark areas are provided as desired.

Thus in the past, silver plated articles have been fully oxidized throughout the silver plated areas and thereafter some of the oxidation has been removed selectively to reveal the original silver plate.

DISCLOSURE OF THE INVENTION tin. Hence manufacturers have not used it as a plating.

material and have continued to use the muchmore expensive silver. By the method of this invention, it is PCS.

sible to secure adequate results by oxidizinga tin plated article. In production, the tinplated: articles, subsequently oxidized, may be treated exactly as silver plated articles. To the layman, the tin plated article is indistinguishable from the silver plated/article. Hence tin is used instead of silverand a very substantial saving in cost is thus accomplished and perfectly satisfactory.

finishes are produced which are varied from. dark gray to light gray. Such finishes may produce the effect commonly referred to as Antique".

One suitable embodiment of the method includes the' following steps.

l. The metal article which may be of almost any suitable metal in almost any desired shape, is plated with tin. This may be accomplished by a conventional chemical process. Frequently the parts used will be of steel, or they may be die cast of any metal suitable for die casting. The tin plating may be carried out by any conventional tin plating method and this invention is not limited, therefore, to any particular method of tin platmg. I I

Where it is desired to produce a particularly smooth finish on the article, the article may be copper plated first and subsequently nickel plated and finally tin plated; or the article may be merely copper plated and then tin plated. Whether or not there is merely a tin plating, or a prior plating with copper,'or copper and nickel,.-the subsequent steps of the method'are the same. For the method, it"is essential onlythat the article be tin plated. i

2. After the tin plating step has been accomplished, the article is rinsed in cold water. This is primarily to remove from it any solution which may remain after the plating step has been accomplished.

3. The tin plated and suitably washed article is thereafter activated in a hydrochloric acid solution with an electric current. The articles to be activated are positioned as the cathodes in the electrical circuit.

The activating step is carried out in a hydrochloric acid solution preferably of 5 to 15 percent hydrochloric acid by volume. While suspended in the hydrochloric acid bath, the articles are subjected to a direct current electricity of a current density of two to ten amperes per square foot of the area of the article to be activated. The activation step is accomplished in a time of five seconds to one minute. The step which is called activation modifies the tin plate and makes it susceptable to oxidation.

4. After the activation of step 3, the article is rinsed in cold water sufficiently to remove the hydrochloric acid solution.

5. After cleansing in the cold water washing step, the article is oxidized until the desired color has been obtained. The oxidizing is accomplished by placing the article in an oxidizing bath. One typical oxidizing solution is formed as follows:

lead acetate 3 oz. per gallon of water sodium thiosulphate 7 oz. per gallon of water acetic acid 4 oz. per gallon of water The temperature of the oxidizing bath is preferably between F. and F. This produces a uniform andsatisfac'tory coloring of the article.

The article is allowed to remain in the oxidizing bath until it has produced a suitable color anda suitable density of-color. The oxidation acts upon the activated tin plate, coloring the article and producing a blue color. It will' be light blue if the time is short during which-the 'partis in the oxidizing bath, anda deeper blue color'will be produced'if the part is leftlonger in the oxidizing bath.

6. The article is initially washed in cold water after removal from the oxidizingbath to remove the oxidizing liquid from the part.

7. After cold waterrinsing'or washing, the part is again rinsed in hot water to complete the cleaning and removal of the oxidizing bath fluid.

8. After the hot water rinse, the part is treated by the application of a wire wheel and powder pumice abrasive to remove as much of the color as is desired. This treatment will normally be carried out to remove much of the color and to leave only blue in details which will have a shaded or shadowed effect as desired. During the application of the wire wheel brush, the oxidization color which is allowed to remain tends to become grayish so that the article after treatment will have a grayish appearance at all points where the oxidation remains and will have the bright tin color where the oxidation has been removed.

The shaded or shadowedareas which remain after the wirev wheel brushing treatment are in that part of the area of the article which has not been specifically wire brushed. .Some overlapping of the wire wheel brush into the areas which are to be left shaded will occur. This overlapping" does not remove the oxidation but the blue color isturned gray.

While generally a satisfactory'article can be obtained by carrying out the steps enumerated above, it has been found that stains may appear and that water contaminents may not be readily rinsed from the plated parts. The degree of brightness of the tin plate may make it difficult or impossible to obtain the desired color. Also, any irregularity in the tin plating may become permanent in the finished article. To prevent these unsatisfactory results and to insure a proper final appearance on the finished article, it has been found useful to treat the parts by wire brushes with clear cold water before the activation process of Step 3 is carried out. This wire brush treatment on the tin plated article before activation has the following useful effects.

1. It tones down the brightness of the tin plate and give the part a semibright appearance which may be readily controlled and duplicated in production.

2. The wire brushing after the completion of tin plating removes stains which may be present after rinsing and which are probably caused by natural elements contained in the water used for rinsing or by contaminents that are introduced in the water during the normal plating cycle.

3. irregularities in the tin plated part which may remain after the completion of the plating are blended by the wire brush. Among the irregularities which may remain after plating and rinsing and which are removed by the wire brush are contaminents in the tin plating bath which may be deposited during the tin plating cycle. These contaminents are unsightly and may be detrimental to the final oxidation process and the wire brush either removes them or so blends them throughout the surface of the article that they will not be noticeable after oxidizing.

To insure a uniform blue finish, when that color is desired on the completed article, this wire brushing of the plated article before activation is very desirable and may be considered essential for successful uniform commercial production where the blue color is to remain on the final article as it is sold for use. When the article is to be antiqued so that it will not retain the blue color as finally put into use, it is not necessary to carry out the wire brush treatment prior to activation, although it may be done without detriment to the quality of the article.

The activating step is essential for uniform production of both forms of the article whether the article is finally to retain the blue color or is finally to be antiqued by the removal of most of the oxidized material. Although occasionally some oxidizing will occur or can occur without the prior activating step, this rarely occurs and cannot be relied upon for commercial production which requires the activating step before oxidation. The activating step appears, therefore, to be necessary for consistent and uniform color in useful commercial production.

If desired, the final article, after completion of all the steps above, may be given a coating of transparent lacquer which does not alter the color or appearance of the article but which may act as a protective coating when the article is used.

I claim:

1. A method of providing a desired finish on a metallic article including the steps of:

plating the metallic article with tin,

washing the article after the tin plating process,

placing the metallic article in a 5 to 15 percent by volume hydrochloric acid solution and with the article forming the cathode in an electric current path applying a direct current of a density of two to ten amperes per square foot of the article for a time of five seconds to one minute through the solution,

washing the article,

placing the tin plated article in an oxidizing solution until a desired color has been obtained,

washing the article,

and thereafter mechanically removing desired amounts of oxidized tin plate on portions of the article to produce a desired tone and color of finish.

2. The method of claim 1 further characterized by the fact that the oxidizing solution comprises approximately 3 oz. per gallon of water of lead acetate, approximately 7 oz. per gallon of water of sodium thiosulphate and approximately 4 oz. per gallon of water of acetic acid; all three components being dissolved in water.

3. The method of claim 2 further characterized by the fact that the temperature of the oxidizing solution is of the order of F. to F.

4. The method of claim 1 further characterized by the fact that the article is finally treated for the removal of some oxidation by means of a rotary abrasive brush and a powdered abrasive.

5. The method of claim 1 further characterized by the fact that the tin plated article is treated with a wire brush prior to placing it in the hydrochloric acid solu- 

2. The method of claim 1 further characterized by the fact that the oxidizing solution comprises approximately 3 oz. per gallon of water of lead acetate, approximately 7 oz. per gallon of water of sodium thiosulphate and approximately 4 oz. per gallon of water of acetic acid; all three components being dissolved in water.
 3. The method of claim 2 further characterized by the fact that the temperature of the oxidizing solution is of the order of 130*F. to 165*F.
 4. The method of claim 1 further characterized by the fact that the article is finally treated for the removal of some oxidation by means of a rotary abrasive brush and a powdered abrasive.
 5. The method of claim 1 further characterized by the fact that the tin plated article iS treated with a wire brush prior to placing it in the hydrochloric acid solution. 